need help with box recommendations

[Marshall Juers 2]

for starters 2002 ford mustang gt double din jvc Big 3 upgrade 250 amp alternator running hifonics brx 2400.1 with 640.4 both brx  changed up build was going to run 1 fi bl 12 dual 1 already ordered and on the way but ran into a fi btl 18dual 2 my game plan is to remove back seat and build sub enclose there web site says 5 to 8 cubes tuned 32 htz got just barely enough room for 7 cubic foot box with amps in trunk lol! Is  it possible to get go low end with 5 cubes trying to open a little area  other wise the 18 is 3 inches from my head in case I didn't say 18 is sub I will use also do have xs battery coming also I guess im asking for help to design size of box and port size and length my area size I can get 40 wide but don't wanna do 22x22 high and deep ant sugguestions please help

 

[ohio45113 24]

if you dont have room for a 18 dont run a 18...